What if I told you that star-shredding black holes could be lurking everywhere in the cosmos, just waiting for us to uncover them? This intriguing revelation comes from a groundbreaking study conducted by scientists at MIT, which is featured today in the Astrophysical Journal.
The team has announced the identification of 18 new tidal disruption events (TDEs)—dramatic occurrences that take place when a star is pulled toward a black hole and violently torn apart. As the black hole consumes the star, it releases a tremendous burst of energy that can be detected across various wavelengths of light.
Traditionally, astronomers have spotted TDEs by focusing on bursts emitted in optical and X-ray wavelengths. Until now, around a dozen of these cosmic events have been cataloged in our nearby universe. However, this new research from the MIT team has more than doubled the roster of known TDEs.
So how did they achieve this? Instead of only analyzing visible light, the MIT researchers turned their attention to infrared wavelengths. These events not only emit light in the optical and X-ray zones but can also radiate in the infrared spectrum, particularly in dust-laden galaxies where the central black hole is surrounded by galactic debris. The dust often absorbs and obscures the lighter wavelengths, making TDEs challenging to detect. Yet, this same dust heats up and emits infrared radiation, which can serve as a beacon for detecting these cosmic phenomena.
By searching the infrared spectrum, the team was able to identify many previously hidden TDEs in galaxies across the universe. These 18 newly discovered events span various types of galaxies scattered throughout the night sky.
“Most of these sources wouldn’t be visible in optical bands,” explains lead author Megan Masterson, a graduate student at MIT’s Kavli Institute for Astrophysics and Space Research. “If we seek to understand TDEs comprehensively and use them to study the demographics of supermassive black holes, we need to pivot our gaze toward the infrared band.”
Other contributors to this research include Kishalay De, Christos Panagiotou, Anna-Christina Eilers, Danielle Frostig, Robert Simcoe, and MIT’s assistant professor of physics Erin Kara, alongside collaborators from several institutions, including the Max Planck Institute for Extraterrestrial Physics in Germany.
Uncovering Cosmic Mysteries
Recently, the team located the closest TDE ever detected by examining infrared data. This milestone discovery opens up a new pathway for astronomers to locate black holes that are actively feeding on stellar matter.
This initial detection drove the researchers to delve deeper in search of additional TDEs. The team utilized archival observations from NEOWISE, the reactivated version of NASA’s Wide-field Infrared Survey Explorer, a satellite launched in 2009 that tirelessly scans the sky for brief infrared transients.
Utilizing an algorithm developed by co-author Kishalay De, the team sifted through the archival data, identifying patterns in infrared emissions likely signifying transient events. They cross-referenced these flagged anomalies with a catalog of known galaxies within 200 megaparsecs (about 600 million light-years), tracing infrared transients to approximately 1,000 galaxies.
Each galactic signal was examined to establish whether it originated from a source other than a TDE, such as an active galactic nucleus or a supernova. After eliminating these alternatives, the team focused on signals exhibiting a distinct pattern characteristic of a TDE—marked by a sharp spike in infrared radiation followed by a gradual decline. This reflects the black hole’s process of ripping apart a star, which rapidly heats the surrounding dust to approximately 1,000 kelvins before it cools down.
The analysis ultimately confirmed 18 clear signals of tidal disruption events, with the team finding these events scattered across a range of galaxy types all over the sky.
“If you look up and see numerous galaxies, TDEs occur in a diverse array of them,” Masterson states. “It’s not just one specific type of galaxy, which was the prevailing belief based solely on optical and X-ray searches.”
“Now, we can peer through the cosmic dust and complete our census of nearby TDEs,” notes Edo Berger, a professor of astronomy at Harvard University who was not involved in the study. “The potential for follow-up studies using extensive infrared surveys is thrilling, and I look forward to the discoveries that may unfold.”
Shedding Light on Cosmic Questions
This research sheds light on several critical issues concerning tidal disruption events. Previously, TDEs were predominantly observed in one type of galaxy—a ‘post-starburst’ system that had transitioned from being a star-forming powerhouse to its current state. Such galaxies are rare, raising questions about why TDEs seemed confined to these systems. Interestingly, these particular galaxies are also relatively free of dust, which makes optical and X-ray emissions easier to detect.
By expanding their search into the infrared spectrum, the MIT researchers could identify TDEs across a much broader range of galaxies. Their findings demonstrate that black holes can consume stars from varied galactic environments, not just those rare post-starburst systems.
Furthermore, the discoveries help address the “missing energy” conundrum. Theoretically, TDEs should emit more energy than has been observed thus far. However, the team suggests that dust may account for this discrepancy; when TDEs occur in dust-rich galaxies, the absorbed emissions—including optical, X-ray, and even extreme ultraviolet radiation—could explain the theorized “missing energy.”
The 18 new detections also provide insights into the frequency of TDEs within galaxies. Incorporating these new findings with earlier detections leads to the estimation that a galaxy experiences a tidal disruption event approximately once every 50,000 years, aligning more closely with physicists’ theoretical predictions. The team is hopeful that increased infrared observations could further clarify the rate of TDE occurrences and the characteristics of the black holes involved.
“Previously, complex theories were proposed to explain these mysteries, but now we have a framework for resolving them,” reveals Kara. “This gives us confidence that exotic physics aren’t necessary to interpret our observations. We are gaining a deeper understanding of how stars are destroyed and consumed by black holes.”
This research was made possible with support from NASA.
Photo credit & article inspired by: Massachusetts Institute of Technology
